package OOscheme.Visitor;
import OOscheme.*;

/**
 * Computes the length of the AList host.
 */
public class GetLength implements IListAlgo {
    /**
     * Singleton Pattern.
     */
    public static final GetLength Singleton = new GetLength();
    private GetLength() {
    }

    /**
     * Returns Integer(0).
     * @param host an EmptyList
     * @param inp not used
     * @return Integer.
     */
    public Object emptyCase(AList host, Object inp) {
        return new Integer(0);
    }

    /**
     * Return the length of the host's rest plus 1.
     * @param host an NEList
     * @param inp not used.
     * @return Integer
     */
    public Object nonEmptyCase(AList host, Object inp) {
        Integer restLen = (Integer)host.getRest().execute(this, null);
        return new Integer(1 + restLen.intValue());
    }
}